This invention relates to a laryngeal-mask airway (LMA) device, which is an artificial airway device designed to facilitate lung ventilation in an unconscious patient by forming a low-pressure seal around the laryngeal inlet. An inflatable-ring seal surrounds an appropriately shaped mask which fits into the lower pharynx and is attached to a tube which emerges from the mouth, as for connection to medical gas-supply tubing.
More particularly, the invention relates to a variety of laryngeal masks, known as gastro-laryngeal masks (GLM), wherein. provision is made for airway assurance to the patient who is at. risk from vomiting or regurgitation of stomach contents while unconscious. U.S. Pat. No. 5,241,956 deals with this problem by providing an evacuation tube which is open through the center of the inflatable seal of the laryngeal mask, thus utilizing the distal end of the inflatable ring as an inflatable-cuff formation which establishes peripherally sealed engagement to the upper sphinctral region of the oesophagus and centrally supports the distal end of the evacuation tube. In addition, said U.S. Pat. No. 5,241,956 discloses a further inflatable cuff carried by the laryngeal mask and by the evacuation tube, for referencing inflation against the back wall of the pharynx, thus making it possible to establish the laryngeal-inlet seal with reduced inflation pressure, as compared with prior structures not having such an additional inflatable cuff.
U.S. Pat. No. 5,305,743 discloses moulding techniques for manufacture of a variety of laryngeal masks, including a gastro-laryngeal mask, wherein an inflatable back cushion provides such referencing inflation against the back wall of the pharynx as to widely distribute the back-wall reference, over substantially the full area of the laryngeal mask. Such a back-cushion construction has been found to be mechanically simple and highly effective, and U.S. Pat. No. 5,355,879 discloses such a back cushion for each of several representative laryngeal-mask constructions.
In practice, although a gastro-laryngeal-mask as described in said U.S. Pat. No. 5,355,879 works well, it has the disadvantage that the gastric evacuation channel needs to be sufficiently stiff to prevent its collapse under the influence of the increased pressure within the back-cushion cuff, when it is inflated in the pharynx. A suitably stiff tube is readily provided, but the whole device is then more difficult to insert into the patient's throat, since insertion involves flexing the device around the angle at the back of the tongue. Provision of a pre-curved airway tube facilitates passage around the back of the tongue, but the advancing distal tip end of the device is then more likely to collide with the glottis (or entrance to the larynx), and indeed it may block the larynx by so doing, with consequent danger to the patient.